Studies in liquid phase adsorption at organic and inorganic surfaces

Hassan, Ahmed S.A (1957) Studies in liquid phase adsorption at organic and inorganic surfaces. PhD thesis, University of Glasgow.

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The first section of the thesis is concerned with adsorption by chitin. Lobster-shell chitin, prepared from the carapace of Nephrops norvegicus, has been used in quantitative adsorption studies with mineral and organic acids and sulphonated azo-dyes in aqueous solutions. In the case of acids the hydrogen ions are adsorbed initially on the acetylamino-groups in the substrate with a consequent swelling and breakage of inter-chain bonds owing to the pressure of solvated water around the resultant cationic centres. The actual amount of acid adsorbed is determined however by the ability of the anion to penetrate the structure. The hydrogen ion can penetrate it readily, but to preserve neutrality each adsorbed hydrogen ion must be accompanied by an anion, and owing to the high crystallinity of chitin the entry of anions is restricted, and in fact the amount adsorbed decreases linearly with the volume of the anion in any given series of acids with similar basic structure. Superimposed on this volume effect, however, is the effect of increased van der Waals attraction of the anion for chitin, with increase in the number of aromatic nuclei in the anion. Generally the affinity rises with increase in length of the conjugated system of the dye molecule. The ion-exchange adsorption process between the chitin and sulph-onate groups of the dye has a negligible apparent heat change, but the non-polar attraction of the remainder of the dye molecule does produce a heat change which increases with the non-polar affinity. Affinity measurements show that one sulphonate group in an adsorbed dye becomes associated with one of the cationic centres in chitin and that additional groups after the first are not so combined and remain dissolved in water, hence decreasing the affinity of the anion for the substrate. Hydrogen-bonding is also operative where there are potential hydrogen-bonding groups in the substrate, but seems to decrease with increasing acidity of the bath. The results of full elementary analyses suggest that chitin does not consist entirely of poly-N-acetylglucosamine, but that about one eighth of the amino-groups are unacetyl-ated. The next section of the thesis describes an investigation made to study and compare the adsorption mechanism of a variety of aromatic compounds, with and without hydrogenbonding groups, by cellulose and by chitin from water and from non-aqueous solvents. In absence of water polar nonionic compounds are adsorbed by both cellulose and chitin principally by hydrogen-bonding. In aqueous solution chitin adsorbs anionic solutes with potential hydrogen-bonding groups principally by ion-exchange and hydrogen-bond formation. Non-polar attraction is also operative in the case of large molecules. Cellulose seems to adsorb these compounds by non-polar attraction only, the affinity increasing with the size of the solute molecule and being independent of the presence therein of hydrogen-bonding- groups. Planar non-hydrogen-bonding anionic compounds are not adsorbed on chitin from alkaline solutions. Cellulose however does adsorb such compounds from either neutral or alkaline solution, because its attraction is non-polar and dependent not on hydrogen-bonding forces, but only on the presence of a highly conjugated system in the solute molecule This work was followed by a study of the adsorptive properties of graphite for organic solutes, mainly dyes, from aqueous and non-aqueous solvents. Rate measurements demonstrate a rapid adsorption and the short period required to reach equilibrium suggests that adsorption is entirely superficial. Basic dyes are quickly adsorbed, by electrostatic attraction. Anionic dyes appear to be adsorbed by physical attraction and the rate of adsorption is higher in the case of dyes which dissociate easily into single molecules. The surface area of graphite was determined by electron microscopy and the orientation of adsorbed molecules studied. At low concentration it seems that most of the compounds used form condensed monolayers. Sulphonated compounds appear to be so oriented that the sulphonate groups are as far away as possible from the graphite surface and non-ionic compounds lie flat so that they present a maximum surface area to the graphite.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: C H Giles
Keywords: Physical chemistry
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-73548
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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